Abstract:

The use of lignocellulosic materials as biosorbents has both environmental and
economic benefits. They are biodegradable, safe to use and most importantly renewable
and less costly. The objectives of this present study were to study the effect of treatment
on the performance of water hyacinth root biomass as a biosobent for n-hydrocarbons
and polar organic solvents. Water hyacinth, a lignocellulosic material was chemically
treated by two methods, nitric acid and organic solvent. The effect of the treatment was
studied by Fourier Transform Infra-red (FT-IR) spectroscopy, Thermogravimetric
analysis, X-ray diffraction (XRD), scanning electron microscopy and other analyses.
FT-IR absorption bands were obtained at 3421, 2855, 1457 and 1035 cm-1 (O-H stretch,
C-H vibration, C-H asymmetric deformation, and C-O stretch, respectively) and 1508,
1541 and 1559 cm-1 (all aromatic skeletal vibrations characteristic of lignin), as well as
a C=O carboxylate stretch vibrational band at 1654 cm-1. The chemical composition
and FT-IR analyses showed that treatment resulted in a decrease in the amount of lignin
in the biomass. X-ray diffraction and scanning electron microscopy confirm the root
biomass to be amorphous and not to have a strongly structured surface. The XRD
revealed that treatment increased crystallinity. Thermogravimetric analysis studies
displayed that the treated biomass is more thermally stable than the untreated biomass.
The surface area of the biomass increased upon treatment. Thermodynamic parameters
for the adsorption of n-alkanes hexane to nonane on ground dried water hyacinth
(Eichhornia crassipes) root biomass were studied between 40oC and 70oC column
temperature using gas solid chromatography, before and after treatment of the root
biomass with mineral acid and organic solvent. The enthalpy of adsorption (Ha) values
of 20.42KJ.mol-1 for hexane to -44.44KJ.mol-1 for nonane were obtained for the
adsorption of the n-alkane series on untreated water hyacinth root biomass. Mineral
acid and organic solvent treatments led to greater adsorption bond strength, with Ha
values of -34.01 to -36.33 kJK-1mol-1 respectively after mineral acid treatment, and -
40.98 to -46.7 kJ.mol-1 after organic solvent treatment. Factors affecting the adsorbentadsorbate
interaction are discussed. The adsorption properties of dried water hyacinth
root biomass towards four polar solvents (dichloromethane, ethylacetate, diethylether,
and acetone) were studied by inverse gas chromatography between 400C and 700C. The
enthalpy of adsorption (Hads) values obtained for the polar probes range from -51.234
for acetone, an amphoteric probe to -74.658 kJ.mol-1 for dichloromethane an acidic
probe for untreated biomass. Mineral and solvent treatments led to reduction in the
values of enthalpy of adsorption due to removal of high energy sites on the surface of
water hyacinth root biomass. The Lewis acidity, Ka, and Lewis basity Kb parameters
were calculated from the net retention volumes, Vn of the probes. The b a K K ratios
for the untreated, acid-treated and organic solvent treated biomass were found to be
9.2175, 6.7425 and 6.5733 respectively, indicating that all the surfaces of the untreated,
mineral acid and organic solvent treated water hyacinth root biomass are basic in nature.